There are many examples where a person wants to know about activities of other people, and possibly cause some action to be taken in respect of those other people. For example, a person may want to learn at least some information concerning how other people have used or interacted with some data.
As a particular example, users often want to know who has read an email message that they sent, perhaps just for general feedback on the interest in the email shown by other users or to allow some contact to be made with those readers of the email. However, the readers are often wary of sharing this information. There are existing features, such as email read reports, but these are only sent at the reading user's option and many users will simply decline to have their reading of the message reported to the sender (for any of a number of reasons, including privacy). Some other examples are document files stored in a shared location within a company, pages on a company's intranet wiki, and even pages on a public website such as Wikipedia for example. The list of users who have edited a shared company document or intranet wiki page is often available to anyone in the company. Similarly, the list of users who have edited a page on a public wiki is generally visible. However, there is generally no information available about who has read a shared document or wiki page or the like. As yet another example, users might also like to contact other users who are working on projects similar to their own, or who have similar interests or competencies. This could be assessed by checking the subject lines of email messages that other users are sending. However, again, the other users will typically be unwilling to have this information made generally available, even within their own organisation.